Key Words and Phrases: - eCommons@Cornell - Cornell University

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B. Cassava:
9assava is grown only in tropical and. subtropical climates, up to about 28" latitude north or
south, and near the equator up to an altitude of about 2,000 masl. Because of its ability to tolerate
low soil fertility and droughty conditions, cassava is generally grown in areas of poor soils and under
conditions of low or irregular rainfall. However, cassava is widely adaptable, and can be grown on
almost any soil type, and with as little as 500 to as much as 3,000 mm. annual rainfall, the latter
only if soils are adequately drained. In Africa it is principally grown in areas of degraded soils, the
results of shortening fallow periods in slash-and-burn agriculture. Under these traditional systems,
cassava is generally intercropped with maize, grain legumes, or vegetables, or it is grown among
banana or coconuts.
The crops found intermixed with cassava vary with geographical areas and
cultural habits (Table 2). Monocropping characterizes the production systems of the major cassavaproducing
countries of Thailand and Brazil, where land preparation tends to be mechanized.
However, cassava is usually grown with little fertilizer and pesticide inputs.
C. Sweet potato:
Sweet potato is a short-maturity (4-6 months) root crop, which is adapted to a wide range of
growing conditions. Roots can remain in the ground for much longer and until time of utilization.
Sweet potatoes are cultivated in the tropics, subtropics and in the warmer areas of the temperature
zone, as well as in the tropical highlands to altitudes of up to 1,800 masl. Because of their ability to
tolerate low soil fertility, sweet potatoes are often grown by small farmers on marginal land. In
China and Vietnam it is usually grown as a winter crop in rotation with summer rice. In that case, it
is grown on mounds or ridges in drained paddy fields with relatively fertile soils.
D. Yam:
Yams can be grown throughout the tropics, but the main center of production is in the savanna
region of West Africa. Yams are rather drought resistant, but require high soil fertility. They are
generally grown only in small plots and are intercropped with other food crops (Table 2). Yams are
usually grown on mounds or ridges on the best soils enriched with compost or animal manure. Yam